1. Field of the Invention
The present invention relates to a mold for a pneumatic tire, more particularly to a mold used with an inflatable bladder which is capable of minimizing air staying between the bladder and tire.
2. Description of Related Art
In general, during vulcanizing a pneumatic tire, as shown in FIG. 8, the inside of the green tire T in a mold (a) is pressured by a bladder (b) inflated by a heating and pressurizing medium. The bladder (b), during inflating, first contacts with the tread portion Tt and bead portion Tb, and as indicated by arrows f1 and f2, the contact region expands toward the sidewall portion. Therefore, air (e) is liable to remain between the bladder (b) and green tire T in the sidewall portion especially near the shoulder portion Ts1. The remaining air (e) partially decreases pressure which presses the green tire T against the mold (a). Therefore, carcass cord tension decreases partially, and accordingly, cord elongations, cord spacings and cord directions are liable to become ununiform, which results in deterioration of tire performances such as steering stability, road noise, force variation, bulge/dent on the tire outside, rubber bare and the like.
It is therefore, an object of the present invention to provide a tire mold for use with a bladder which can minimize air between the bladder and green tire.
According to the present invention, a tire mold comprises a pair of bead rings, each of the bead rings provided with a bead bottom molding face for molding the bead bottom surface of the tire, and further each bead ring provided radially inside the bead bottom molding face with a protrusion protruding axially inwardly from the axially inner end of the bead bottom molding face so that the axial extent of the protrusion from the axially inner end of the bead bottom molding face is in the range of from 0.05 to 0.4 times the axial distance between the axially inner ends of the bead molding faces.